1. Technical Field
The invention relates to the field of night vision devices, and particularly to a system for combining images from an image intensifier and an infrared camera system.
2. Background Art
Standard night vision is enhanced with the addition of IR information. Whereas typical night vision devices (image intensifiers) can only see visible wavelengths of radiation, the fused system provides additional situational awareness by providing infrared (heat) information to the image. A typical scenario where this might be important is in a situation where a person is camouflaged and cannot be seen with image intensification. However, with the addition of infrared information to the same image, the camouflaged person""s heat signature is seen. Typical infrared night vision devices do not have sufficient resolution and sensitivity to provide good imagery of the full environment being looked at. Use of overlay image intensification (II) and infrared radiation (IR) fusion provides benefit of II resolution and environment awareness with benefit of infrared signatures, smoke penetration, etc.
Generally, there are two alternative methods of fusion: digital fusion and analog fusion.
Previous designs for combining images have used a dichroic beam splitter. The image intensifier image would pass directly through the beam splitter while the infrared image projected by a display would reflect off the beam splitter and merge onto the image intensifier image.
One technique known for combining an infrared image with an image displayed at visible wavelengths is described in U.S. Pat. No. 4,751,571 to Lillquist. The system disclosed in this patent has two separate image paths. One path transmits visible light to an image intensifier while a second path transmits thermal IR to an IR detector. Both the intensified image and the IR image are converted to electronic video signals. The two electronic signals are then mixed at a video mixer and then displayed on a color monitor. The technique described in the Lillquist patent has the disadvantage of requiring that both signals be electronically converted and electronically combined before being displayed to a user. Such electronic conversion will lose the very high resolution of the image intensified night vision device. Additionally, the Lillquist approach requires a dedicated system not usable with the vast population of existing night vision devices.
Another image fusion system is described in U.S. Pat. No. 5,035,472 to Hansen. This patent describes a device that conveys the image along two separate paths. One path directs the image to an IR detector which produces an IR image. The IR image is then transmitted to a CRT which displays the image. A second path directs the image of the scene to an image intensifier tube which generates an intensified image which also produces a visual display of the image. The displayed IR and intensified images are optically combined for display to a user. The technique described in the Hansen patent requires both images to be visibly generated before they are optically combined behind the image intensifier. This approach has the disadvantage of requiring a dedicated system not usable with the vast population of existing night vision devices.
Another technique calls for detecting a scene using multiple sensors which convert the images to digital data and then algorithmically combine the data using microelectronic processors. The disadvantages of this approach are that it is time consuming, requires substantial processing power, and the high resolution of a night vision channel cannot be captured electronically.
Prior designs typically use a dichroic beam splitter. The image intensifier image passes directly through the beam splitter while the infrared image projected by a display would reflect off the beam splitter and merge onto the image intensifier image. Use of the beam splitter in such prior designs adds weight, size, forward projection as well as requiring additional parts to hold the beam splitter assembly.
While the above cited references introduce and disclose a number of noteworthy advances and technological improvements within the art, none completely fulfills the specific objectives achieved by this invention.
In accordance with the present invention, a system for combining multi-spectral images of a scene includes a first channel or detector for transmitting a scene image in a first spectral band. A separate, second detector senses the scene in a second spectral band. The second detector has an image output that is representative of the scene. A transparent display mounted in the output viewing path of the first detector and displays a displayed image in the second spectral band. The image of the transparent display is aligned such that the image of the scene in the second spectral band combines with the image output in the first spectral band. The combined multi-spectral images are conveyed to an output for a user.
An object of the present invention is to provide a means to fuse an image intensifier and an IR camera image using optical overlay methods while minimizing the weight, size, form factor, goggle forward projection of the night vision goggle assembly.
These and other objects, advantages and features of this invention will be apparent from the following description taken with reference to the accompanying drawings, wherein is shown the preferred embodiments of the invention.